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to this second part of my talk
on studying human aging.
As trailed at the end of the first part,
I'm going to discuss three examples
in order to help you
apply the lessons you've learned
from the methodological issues
we discussed in the first half
of this talk.
Now I'd like, in the next few slides,
to give you three examples
to draw together
some of the themes that we've discussed
around in the way aging develops
and the challenges of measuring
aging in humans
and the challenges
of undertaking robust study designs.
Now the first example
is about calorie restriction.
Now calorie restriction in animals,
restricting their diet to such an extent
that they remain healthy
and have a balanced diet
and have very little adiposity.
That has been shown repeatedly
to increase longevity
in most mouse models.
I'm sure this will be covered
in some of the other talks
in this course.
It's very clear from mouse experiments
that being lean increases survival.
And the same is pretty true in humans,
humans in the normal weight range,
so a body mass index from 18.5 to 25
have lower mortality than those
who are overweight or obese in midlife,
and obesity and being overweight
clearly increases mortality
and a whole range of disease
there's a major apparent paradox
of obesity in later life.
For example, Flegal et al.,
meta-analyzed a huge number
of studies of obesity
and reported that grade 1 obesity,
that's body mass indexes
between 30 and 35
overall were associated
with high mortality
in 65-year-olds and older.
How is it possible
that the experimental data
shows that obesity is bad for you
and the observational data
in later life shows the opposite?